(a) Field of the Invention
The present invention relates to novel disazo compounds, a process for the preparation of the same, and application of said disazo compounds as well as analogues thereof to electrophotographic sensitive materials.
(b) Description of the Prior Art
It is known that some organic compounds, for instance, indigo-type compounds, phthalocyanine-type compounds, etc. are useful as a photoconductive material for preparing photosensitive materials for use in the electrophotographic process. The "electrophotographic process" herein is one of the image-forming process which generally comprise first charging a photo-conductive sensitive material with the electric charge by corona discharge or the like in the dark, subsequently subjecting it to image-wise exposure so as to discharge the electric charge of the exposed area selectively, thereby obtaining an electrostatic latent image, and then rendering visible this latent image area by a developing means employing a toner, etc., thereby forming an intended image. As the fundamental characteristics required for the photosensitive materials for use in such an electrophotographic process, there are enumerated (1) an appropriate chargeability in the dark, (2) a low dischargeability in the dark, and (3) a rapid dischargeability upon exposure to light. As a matter of fact, however, the known photoconductive organic compounds have not always sufficiently satisfied these requirements.
As applicable photoconductive materials, there are known inorganic materials such as selenium, zinc oxide, etc., of which selenium has admittedly been widely put to practical use. However, with the adoption of various processes in the latest electrophotographic processes, there is an increasing demand for, for instance, a belt-shaped photosensitive material or the like having the aforementioned fundamental characteristics as well as a satisfactory flexibility with respect to the shape thereof. In this regard, the foregoing selenium is generally difficult to form into a photosensitive material having such a shape as above.
Meanwhile, there are known electrophotographic sensitive materials prepared by forming a photosensitive layer containing some azo compound, as an effective ingredient, on a conductive support; for instance, one prepared by employing monoazo compound has been disclosed in Japanese Patent Publication No. 16474/1969, and ones prepared by employing benzidine-type disazo compound have been disclosed in U.S. Pat. Nos. 3,898,048 and 4,052,210. The azo compounds mentioned in these literatures are admittedly useful materials as an effective ingredient of the photosensitive layer, but when various requirements for photosensitive materials are taken into account from the view point of the electrophotographic process, there has in fact not yet been obtained such a material as will sufficiently meet these requirements. Therefore, it is desirable to find a wide variety of compounds, not limited to azo compounds, and which are effective for use in electrophotographic sensitive materials so as to make it possible to select an appropriate one, and in this way, it will become possible for the first time to provide photosensitive material apposite to a certain specific process.